KR20070080696A - Nitride based semiconductor laser diode - Google Patents

Abstract

A nitride based semiconductor laser diode is provided to enhance beam quality by suppressing the loss of an optical mode and to control an OCF(Optical Confinement Factor) or an FFP(Far Field Pattern) by adjusting a thickness of a lower clad layer. A nitride based semiconductor laser diode includes a substrate(100), a lower contact layer(110), upper and lower clad layers(170,120), upper and lower optical waveguide layers(150,130), an activation layer(140), and an electron shielding layer(160). The lower contact layer(110) is formed on the substrate. The lower clad layer(120) is formed on the lower contact layer(110) and has a refraction rate which is equal to or more than one of the lower contact layer(110). The lower optical waveguide layer(130) is formed on the lower clad layer(120). The activation layer(140) is formed on the lower optical waveguide layer(130). The upper optical waveguide layer(150) is formed on the activation layer(140). The electron shielding layer(160) is formed on the upper optical waveguide layer(150). The upper clad layer(170) is formed on the electron shielding layer(160).

Description

Nitride-based semiconductor laser diodes

1 shows a schematic cross-sectional view and a refractive index profile of a nitride semiconductor laser diode according to a first embodiment of the present invention.

FIG. 2 is a graph illustrating an OCF according to a thickness of a lower clad layer of the nitride semiconductor laser diode of FIG. 1.

FIG. 3 shows the half width of FFP according to the thickness of the lower clad layer of the nitride semiconductor laser diode of FIG. 1.

4 shows a schematic cross-sectional view and a refractive index profile of a nitride semiconductor laser diode according to a second embodiment of the present invention.

5A to 5C are graphs showing experimental results of nitride semiconductor laser diodes manufactured according to Comparative Examples.

6A and 6B are graphs showing experimental results of a nitride semiconductor laser diode manufactured according to an embodiment.

<Description of Symbols for Major Parts of Drawings>

100,200 ... substrate 110 ... bottom contact layer

120,220 Lower cladding layer 130,230 Lower waveguide layer

140,240 ... active layer 150,250 ... top waveguide

160,260 ... Electronic barrier layer 170,270 ... Upper clad layer

The present invention relates to a nitride-based semiconductor laser diode, and more particularly to a nitride-based semiconductor laser diode in which the loss of the optical mode is suppressed to improve the beam quality of the laser light.

BACKGROUND OF THE INVENTION Semiconductor laser diodes are widely used as a means for transmitting data or recording and reading data in a communication field such as optical communication or a device such as a compact disc player (CDP) or a digital multifunction disc player (DVDP).

In particular, nitride-based semiconductor laser diodes can be used in a wide range of applications, such as high density optical information storage and reproduction, high resolution laser printers, and projection TVs by making wavelengths available from green to ultraviolet light. have.

In general, a nitride-based semiconductor laser diode is formed by sequentially stacking an n-type contact layer, an n-type cladding layer, an active layer, and a p-type cladding layer on a substrate. The laser light generated in the active layer is constrained by the difference in refractive index and the optical gain is obtained. It has a structure that can reap.

Here, some components of the laser light confined in the active layer may leak to the n-type cladding layer or the p-type cladding layer. In the case of a conventional nitride-based semiconductor laser diode, since the refractive index of the n-type contact layer is generally higher than that of the n-type cladding layer, the leakage component of the laser light directed to the n-type cladding layer is propagated toward the substrate without disappearing. The leakage of the optical mode occurs.

This leakage of the optical mode causes the beam quality of the laser light to be degraded, such as generating ripple in the far field.

To reduce the leakage of the optical mode, it is necessary to reduce the laser light leaking to the n-type cladding layer or to prevent the laser light leaking to the n-type cladding layer from propagating toward the substrate. To this end, the conventional nitride-based semiconductor laser diode to increase the composition of aluminum (Al) in the n-type cladding layer having the composition of AlxCa1-xN (0 <x <1) to suppress leakage from the active layer to the n-type cladding layer, or The thickness of the cladding layer was made thick so that the light leaked into the n-type cladding layer was sufficiently extinguished before propagating to the substrate. However, if the composition of the aluminum of the n-type cladding layer is increased or the thickness thereof is increased, there is a problem in that cracks are more likely to occur during growth.

In addition, in the case of the conventional nitride-based semiconductor laser diode, the longer the wavelength of the laser light from purple to blue or green, the higher the leakage of the optical mode, so that the beam quality is severely impaired, thus causing serious problems in application to display light sources. Can be.

Accordingly, an object of the present invention is to provide a nitride-based semiconductor laser diode in which the leakage of the optical mode toward the substrate direction is suppressed to improve the beam quality of the laser beam.

In order to achieve the above object, the nitride-based semiconductor laser diode according to the first embodiment of the present invention is grown on a substrate and sequentially stacked with a lower contact layer, lower cladding layer, active layer, upper cladding layer The refractive index of the lower clad layer is equal to or greater than the refractive index of the lower contact layer.

In order to achieve the above object, the nitride-based semiconductor laser diode according to the second embodiment of the present invention is a nitride-based semiconductor laser diode grown on a substrate and sequentially stacked into a lower clad layer, an active layer, an upper clad layer, the lower The refractive index of the cladding layer is the same as or greater than the refractive index of the substrate.

Hereinafter, a nitride based semiconductor laser diode according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this process, the thicknesses of layers or regions illustrated in the drawings are exaggerated for clarity.

FIG. 1A is a schematic cross-sectional view of a nitride semiconductor laser diode according to a first embodiment of the present invention, and FIG. 1B illustrates a refractive index profile of each semiconductor layer constituting the nitride semiconductor laser diode. do.

Referring to the drawings, the nitride-based semiconductor laser diode according to the first embodiment of the present invention on the substrate 100, the lower contact layer 110, lower cladding layer 120, lower optical waveguide layer 130, active layer ( 140, the upper optical waveguide layer 150, the electron blocking layer 160, and the upper cladding layer 170 are sequentially stacked. Here, the lower clad layer 120 has a refractive index equal to or greater than the refractive index of the lower contact layer 110. Although not shown in the drawings, first and second electrode layers may be formed on the bottom surface of the substrate 100 and the top surface of the upper clad layer 170, respectively. The first and second electrode layers may be n-type electrode layers and p-type electrode layers, respectively.

As the substrate 100, a sapphire substrate may be used.

The lower contact layer 110 and the lower clad layer 120 are sequentially stacked on the upper surface of the substrate 100.

The lower contact layer 110 may be formed of an n-type Al x Ga 1-x N compound semiconductor, and an average composition of aluminum (Al), which is a member element thereof, may be in a range of 0 ≦ x ≦ 0.1.

The lower clad layer 120 may be formed of an n-type AlyGa1-yN compound semiconductor. In a compound semiconductor having AlGaN composition, in general, the larger the composition of Al, the smaller the refractive index of the material. Therefore, the average composition (y) of aluminum (Al) of the lower clad layer 120 is such that the refractive index of the lower clad layer 120 is equal to or larger than that of the lower contact layer 110. It is preferable that the average composition (x) of aluminum (Al) of (110) is equal to or less than. That is, the average composition of aluminum (Al), which is a member of the lower contact layer 110 and the lower cladding layer 120, is preferably in the range of 0 ≦ y ≦ x ≦ 0.1. Due to the composition as described above, the leakage component propagated toward the lower clad layer 120 may no longer propagate in the lower contact layer 110, and the leakage of the optical mode may be suppressed.

In general, in the nitride-based semiconductor laser diode, in order to increase the constraint of the optical mode, it is necessary to increase the aluminum (Al) composition of the clad layer or increase its thickness. However, the optical mode is not sufficiently constrained due to a crack generation problem or difficulty in crystal growth, and some optical mode components leak into the clad layer. Accordingly, in the present invention, the refractive index of the lower clad layer 120 is equal to or larger than the refractive index of the lower contact layer 110, so that the leakage component propagated toward the lower clad layer 120 no longer propagates in the lower contact layer 110. It can not be extinguished, and the effect of strongly constraining the optical mode can be obtained. In addition, since AlGaN having a low composition of aluminum (Al) is used as the material of the lower clad layer 120, the possibility of cracking may be reduced.

Meanwhile, the lower clad layer 120 is formed by alternately stacking n-type Aly'Ga1-y'N layers having different composition ratios y 'of aluminum (Al) as well as a single layer structure of n-type AlyGa1-yN. It may have a multilayer structure. For example, the lower clad layer 120 may have a structure in which Al0.08Ga0.92N / GaN layers are repeatedly stacked. The stacked structure of the plurality of layers reduces the incidence of cracking, thereby stably crystallizing the lower clad layer 120.

A lower waveguide layer 130 is formed on an upper surface of the lower clad layer 120, and the lower waveguide layer 130 may be formed of an n-type In x Ga 1-x N (0 ≦ x ≦ 0.2) compound semiconductor. In addition, an active layer 140 is formed on an upper surface of the lower waveguide layer 130, and the active layer 130 may be formed of an In x Ga 1-x N (0 <x <1) compound semiconductor. Here, the active layer 130 may have a structure of any one of multiple quantum wells or a single quantum well. An upper waveguide layer 150 is formed on an upper surface of the active layer 140, and the upper waveguide layer 150 may be formed of a p-type In x Ga 1-x N (0 ≦ x ≦ 0.2) compound semiconductor. Meanwhile, an electron blocking layer 160 is formed on the upper surface of the upper waveguide layer 150 to prevent electrons from overflowing. The electron blocking layer 160 is formed of AlxGa1-xN. (O <x <1) compound semiconductor. In addition, an upper cladding layer 170 is formed on an upper surface of the electron blocking layer 160, and the upper cladding layer 170 has a p-type Al x Ga 1-x N (0 <x <1, preferably 0.01 ≦ x ≦ 0.1) may be made of a compound semiconductor.

As described above, the lower clad layer may be formed by increasing the average composition x of the aluminum Al of the lower contact layer 110 to be equal to or larger than the average composition y of the aluminum Al of the lower clad layer 120. 120 may have a refractive index equal to or greater than the refractive index of the lower contact layer 110, thereby suppressing the loss of the optical mode in the active layer 140. As the optical mode is effectively constrained, ripple generation in the far field of the laser light can be suppressed and the beam quality can be improved.

Further, the laser light characteristics are changed by adjusting the thickness of the lower cladding layer 120 by adjusting an optical confinement factor (hereinafter referred to as OCF) or a far field pattern (hereinafter referred to as FFP). You can.

FIG. 2 is a graph showing OCF according to the thickness of the lower cladding layer, and FIG. 3 is a graph showing full width at half maximum (FWHM) value of the FFP according to the thickness of the lower cladding layer. The data is n-type Al0.01Ga0.99N as the bottom contact layer, n-type GaN as the bottom clad layer, n-type In0.03Ga0.97N thickness 600Å as the lower waveguide layer, In0.15Ga0.85N / In0.04Ga0 as the active layer. It is measured using a nitride-based semiconductor laser diode having a 96N multi-quantum well structure, a p-type In0.03Ga0.97N of 600 kW as an upper waveguide layer, and a p-type Al0.02Ga0.98N of 5000 kW thick as an upper clad layer.

Referring to FIG. 2, it can be seen that sufficient OCF for laser light oscillation can be obtained using n-type GaN as the lower clad layer.

Further, in the nitride-based semiconductor laser diode of the present invention, since the refractive index is controlled regardless of the thickness of the lower clad layer to suppress leakage of the optical mode, as shown in FIG. 3, the FFP is controlled by adjusting the thickness of the lower clad layer. Can be.

In a modification of the above-described embodiment, the lower clad layer 120 (in FIG. 1) may be formed of n-type InyGa1-yN. In this case, the average composition of aluminum (Al) of the lower contact layer 110 formed of n-type Al x Ga 1-x N is in a range of 0 ≦ x ≦ 0.1, and the average composition of indium (In) is in 0 ≦ y ≦ 0.1. It is preferable. By such a composition, the lower clad layer 120 may have a refractive index equal to or greater than that of the lower contact layer 110, and the constraint of the optical mode on the active layer 140 may be enhanced. As a result, ripple generation in the far field of the laser light can be suppressed and the beam quality of the nitride semiconductor laser diode can be improved. The lower clad layer 120 may have not only a single layer structure but also a multilayer structure in which n-type Iny′Ga1-y′N layers having different composition ratios y ′ of indium (In) are alternately stacked.

FIG. 4A is a schematic cross-sectional view of a nitride semiconductor laser diode according to a second embodiment of the present invention, and FIG. 4B shows a refractive index profile of each semiconductor layer constituting the nitride semiconductor laser diode. do.

Referring to the drawings, the nitride-based semiconductor laser diode according to the second embodiment of the present invention, the lower clad layer 220, the lower optical waveguide layer 230, the active layer 240, the upper optical waveguide layer 250 on the substrate 200 And the upper cladding layer 270 are sequentially stacked. Here, the lower clad layer 210 has a refractive index equal to or greater than the refractive index of the substrate 200. Although not shown in the drawings, first and second electrode layers may be formed on the bottom surface of the substrate 200 and the top surface of the upper clad layer 270, respectively. The first and second electrode layers may be n-type electrode layers and p-type electrode layers, respectively.

As the substrate 200, a GaN substrate may be used.

Unlike the above-described embodiment, the lower clad layer 220 is stacked on the upper surface of the substrate 200 without the lower contact layer. The lower waveguide layer 230, the active layer 240, the upper waveguide layer 250, the electron blocking layer 260, and the upper cladding layer 270 are sequentially stacked on the upper surface of the lower clad layer 220. Each of these layers is substantially the same as the corresponding layer of the above-described embodiment, and thus a detailed description thereof will be omitted.

The lower clad layer 120 may be formed of a compound semiconductor of n-type InyGa1-yN, and the average composition of indium (In) may be in a range of 0 ≦ y ≦ 0.1.

By such a composition, the lower clad layer 220 has a refractive index equal to or greater than that of the substrate 210. Accordingly, the leakage component propagated toward the lower clad layer 220 is no longer propagated in the substrate 200 and disappears, thereby strongly constraining the optical mode, suppressing the ripple generation in the far field of the laser light and reducing the beam quality. Can improve. In addition, since GaN or InGaN is used as the material of the lower clad layer 220, there is an advantage that the temperature of crystal growth can be lowered.

Meanwhile, the lower clad layer 220 has not only a single layer structure of n-type InyGa1-yN, but also a structure in which a plurality of n-type Iny'Ga1-y'N layers having different composition ratios y 'of aluminum are alternately stacked. It can have The lower clad layer 220 having a structure in which the plurality of layers are stacked reduces the incidence of cracking, thereby stably growing the crystal.

<Example>

In accordance with the first embodiment of the present invention, a nitride-based semiconductor laser diode was fabricated. Referring back to FIG. 1, a sapphire substrate was used as the substrate 100. An n-type Al0.02Ga0.98N was formed as the lower contact layer 110. An n-type Al 0.01 Ga 0.99 N was formed as the lower clad layer 120. As the lower waveguide layer, n-type In0.03Ga0.97N having a thickness of 600 Å was formed. As an active layer, a multi-quantum well structure of In0.15Ga0.85N / In0.04Ga0.96N was formed. A p-type In0.03Ga0.97N of 600 kV was formed as an upper waveguide layer. Al 0.02 Ga 0.98 N was formed as an upper clad layer.

Comparative Example

As a comparative example, a conventional nitride-based semiconductor laser diode having a refractive index smaller than that of the lower contact layer was fabricated using n-type GaN as the lower contact layer and Al0.15Ga0.85N as the lower clad layer. Except for the lower contact layer and the lower clad layer, the same conditions as in the above embodiment.

With reference to FIGS. 5A and 5B and FIGS. 6A to 6C, the experimental results of the examples and the comparative examples will be compared and described.

FIG. 5A is a graph showing refractive index and light intensity for each layer of the nitride semiconductor laser diode fabricated according to the comparative example, and FIG. 5B is a graph showing the FFP of the comparative example.

The light intensity is expressed in arbitrary units (a.u.). Referring to the drawings, the nitride semiconductor laser diode of the present comparative example shows a conventional refractive index distribution in which the refractive index (n lower clad layer) of the lower clad layer is smaller than the refractive index (n lower contact layer) of the lower contact layer. Accordingly, it can be seen that the leakage component of the optical mode propagated toward the lower clad layer is propagated to the lower contact layer, so that the light restraint is weakened. This optical mode leakage causes ripples in the far field, as shown in FIG. 5B, resulting in poor beam quality.

5C is a graph showing the loss of the optical mode according to the laser light wavelength of the nitride semiconductor laser diode fabricated according to the present comparative example. Referring to the drawings, it can be seen that as the wavelength of the laser light is increased from purple to blue or green, leakage of the optical mode is increased. Since the leakage of the optical mode severely impairs the beam quality, it may be a serious problem in an application to a display light source that requires light of various wavelengths.

6A is a graph showing refractive index and light intensity for each layer of the nitride semiconductor laser diode fabricated according to the embodiment, and FIG. 6B is a graph showing the FFP of the embodiment.

Referring to the drawings, the refractive index (n 'lower clad layer) of the lower cladding layer is larger than the refractive index (n' lower contact layer) of the lower contact layer, it can be seen that the profile of the light intensity has a smooth curve. This means that the leakage component propagated toward the lower clad layer is no longer propagated in the lower contact layer and disappears, so that the optical mode is strongly constrained. As the optical mode does not leak in this way, no ripple is generated at a long distance, the light intensity is smoothly distributed, and the beam quality of the laser beam is excellent.

Furthermore, in the present embodiment, since the leakage of the optical mode does not occur, the phenomenon that the leakage of the optical mode according to the wavelength, which is a problem of the comparative example, does not occur. This means that the beam quality of the laser light can be maintained in various wavelength bands such as blue, green, and the like, particularly in the long wavelength band.

As described above, the nitride-based semiconductor laser diode according to the present invention has the following effects.

First, the beam quality of the laser light can be improved by suppressing leakage of the optical mode toward the substrate.

Second, OCF or FFP can be controlled by adjusting the thickness of the lower clad layer.

Third, since the leakage of the optical mode can be prevented irrespective of the wavelength of the laser light, the beam quality of the laser light can be maintained in various wavelength bands, and is particularly advantageous for improving the beam quality in the long wavelength band.

Such a nitride-based semiconductor laser diode of the present invention has been described with reference to the embodiment shown in the drawings for clarity, but this is only an example, and those skilled in the art have various modifications and other equivalent implementation therefrom. It will be appreciated that examples are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

Claims (11)

In the nitride-based semiconductor laser diode grown on the substrate and sequentially stacked with a lower contact layer, lower cladding layer, active layer, upper cladding layer, And a refractive index of the lower clad layer is equal to or larger than that of the lower contact layer. The method of claim 1, The lower contact layer is formed of AlxGa1-xN, the lower clad layer is formed of AlyGa1-yN, and the average composition of the aluminum (Al) is in the range of 0≤y≤x≤0.1 Semiconductor laser diode. The method of claim 2, The lower clad layer has a single layer structure, or a nitride-based semiconductor laser diode, characterized in that a multi-layer structure in which the layers having different composition ratios of aluminum (Al) are alternately stacked. The method of claim 1, The lower contact layer is formed of AlxGa1-xN, the lower clad layer is formed of InyGa1-yN, and the average composition of aluminum (Al) is in a range of 0≤x≤0.1, and the indium (In) A nitride-based semiconductor laser diode, characterized in that the average composition is 0≤y≤0.1. The method of claim 4, wherein The lower clad layer has a single layer structure, or a nitride-based semiconductor laser diode, characterized in that a multi-layer structure in which layers having different composition ratios of indium (In) are alternately stacked. The method of claim 1, The substrate is a nitride-based semiconductor laser diode, characterized in that the sapphire substrate. In the nitride-based semiconductor laser diode grown on the substrate and sequentially stacked into a lower clad layer, an active layer, an upper clad layer, And a refractive index of the lower clad layer is equal to or larger than that of the substrate. The method of claim 7, wherein The lower clad layer is formed of In x Ga 1-x N, and the average composition of the indium (In) is a nitride-based semiconductor laser diode, characterized in that 0≤y≤0.1. The method of claim 8, The lower clad layer has a single layer structure, or a nitride-based semiconductor laser diode, characterized in that a multi-layer structure in which layers having different composition ratios of indium (In) are alternately stacked. The method of claim 7, wherein The substrate is a nitride-based semiconductor laser diode, characterized in that formed of GaN. The method according to any one of claims 1 to 10, And a layer between the active layer and the substrate is formed of an n-type semiconductor, and the upper clad layer is formed of a p-type semiconductor.

Images